Won't happen. Nintendo is far too conservative, they are not only an old fashioned Japanese company but they are a Kyoto based company and Kyoto business culture is even more stringent and strict than say Tokyo. They like being a small company employee wise. Makes it easier to micro-manage the company.
If they didn't own Retro outright I think they probably would have dumped Retro too, lol. That studio has been given a lot of chances and come up short in terms of delivering a finished product in an acceptable time frame.
What Nintendo does do is they're basically using Bandai-Namco and Tecmo-Koei as outsourcing studios.